Charging System: Description and Operation

GF07.10-P-1009MMC Alternator Interface Function
- ENGINES 157.9 in MODEL 216.3, 221.0 /1
ENGINES 278.9 in MODEL 216.3, 221.0 /1

Function requirements for alternator interface, general points
- Circuit 87M ON (engine control ON)
- Engine running

Alternator interface, general points
Using the alternator interface, messages are exchanged over the drive LIN (LIN C1) between the alternator (G2) and the ME-SFI [ME] control unit (N3/10), in order to regulate the alternator control response. The ME-SFI [ME] control unit reads in the following sensor and signals for this purpose:
- Crankshaft Hall sensor (B70), engine speed
- On-board electrical system battery (G1), on-board electrical system voltage over "circuit 30"
- Alternator, status via the drivetrain LIN

Function sequence for alternator interface
The ME-SFI [ME] control unit controls the alternator control response, for example, in order to reduce the regulation voltage (charging voltage) when the engine is at idle and the on-board electrical system battery is sufficiently charged

This reduces the engine load, thus also reducing fuel consumption and reduces exhaust gas emissions.

The ME-SFI [ME] control unit controls the following functions:
- Switching on of the ALT depending on the on-board electrical system voltage and the demands from the engine.
- Regulation of the alternator according to performance maps stored in the ME-SFI [ME] control unit. To do this, the control voltage is preset by the ME-SFI [ME] control unit.
- Adapting the control voltage with a delay in the event of frequent load changes at the alternator to stabilize the idling speed.
- Protecting the alternator against overheating.
- Generation of a "circuit 61 signal" (alternator in operation).
- Sending of a recognized fault via the chassis CAN (CAN E) and the backbone CAN (CAN F) to the IC (A1) to actuate the respective warning lamps and message displays.
- Maintains the regulation voltage at a low value and arranges increased charging of the on-board electrical system battery in the deceleration phases (fuel saving)

The alternator performs continuous self-diagnosis and sends the results when requested to the ME-SFI [ME] control unit. This compares the results with other signals (for example, engine rpm, on-board electrical system voltage, time since engine start) and thus detects any alternator faults.

The following faults are identified:
- Line for the alternator interface (drivetrain LIN) has an open circuit or the interface driver in the ME-SFI [ME] control unit is defective (the ALT regulates in this case at 14.3 V).
- Electrical and mechanical faults at alternator:
- Controller or diodes defective
- Stator interruption or short circuit
- Excitation circuit open
- Regulation voltage and charging current not reached
- Regulation voltage too high
- Cracked or loose poly-V belt

Diagnosis
To check the regulation voltage, a battery tester must be used to place a load on the on-board electrical system battery, as the regulation voltage can be significantly reduced when the on-board electrical system battery is fully charged and under no load..

Circuit 61 signal
Using information received by the ME-SFI [ME] control unit over the alternator interface, the "circuit 61 signal" is simulated in the ME-SFI [ME] control unit and issued over the CAN network (e.g. for the IC).